Repeating seismicity in the shallow crust modulated by transient stress perturbations

Recent studies have reported seismic phenomena that are modulated by small stress perturbations (similar to 10 kPa), revealing their critically stressed nature. Such observations have been principally limited to plate interfaces with their occurrence linked to high fluid pore-pressure. In this study, we report observations of nine repeating seismic sources in the shallow crust in Guerrero, Mexico that emit events at rates comparable to other seismic phenomena in low stress environments. Testing their susceptibility to small stress perturbations, we find that all nine sources appear to be modulated by mining activity, tides, and a large slow slip event (Mw 7.5). Our results suggest that the fault conditions necessary for low effective stress seismicity can occur away from plate interfaces. (C) 2016 Elsevier B.V. All rights reserved.